Advanced Configuration and Power Interface Specification

Processor Configuration and Control
8.4.5.5 _TDL (T-state Depth Limit)
This optional object evaluates to the _TSS entry number of the lowest power throttling state that
OSPM may use. _TDL enables the platform to limit the amount of performance reduction that
OSPM may invoke using processor throttling controls in an attempt to alleviate an adverse thermal
condition. OSPM may choose the corresponding state entry in the _TSS as indicated by the value
returned by the _TDL object or a higher performance (lower numbered) state entry in the _TSS
down to and including the _TSS entry number returned by the _TPC object or the first entry in the
table (if _TPC is not implemented). The value returned by the _TDL object must be greater than or
equal to the value returned by the _TPC object or the corresponding value to the last entry in the
_TSS if _TPC is not implemented. In the event of a conflict between the values returned by the
evaluation of the _TDL and _TPC objects, OSPM gives precedence to the _TPC object, limiting
power consumption.
Arguments:
None
Return Value:
An Integer containing the Throttling Depth Limit _TSS entry number:
0 – throttling disabled.
1 – state 1 is the lowest power T-state available.
2 – state 2 is the lowest power T-state available.
…
n – state n is the lowest power T-state available.
In order for the platform to dynamically indicate the limit of performance reduction that is available
for OSPM use, Notify events on the processor object of type 0x82 will cause OSPM to reevaluate
any _TDL object in the processor’s object list. This allows AML code to notify OSPM when the
number of supported throttling states may have changed as a result of an asynchronous event. OSPM
ignores _TDL Notify events on platforms that support P-states unless the platform has limited
OSPM’s use of P-states to the lowest power P-state. OSPM may choose to disregard any platform
conveyed T-state depth limits when the platform enables OSPM usage of other than the lowest
power P-state.
8.4.6 Processor Performance Control
Processor performance control is implemented through three optional objects whose presence
indicates to OSPM that the platform and CPU are capable of supporting multiple performance states.
The platform must supply all three objects if processor performance control is implemented. The
platform must expose processor performance control objects for either all or none of its processors.
The processor performance control objects define the supported processor performance states, allow
the processor to be placed in a specific performance state, and report the number of performance
states currently available on the system.
In a multiprocessing environment, all CPUs must support the same number of performance states
and each processor performance state must have identical performance and power-consumption
parameters. Performance objects must be present under each processor object in the system for
OSPM to utilize this feature.
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